I cannot speak from any experience with this lens or brand, but it seems a little bit too good to be true. I'd question the quality of the Ukrainian optics, as I've heard some pretty mixed reviews about other lenses made in that part of the world. By mixed reviews, I mean that some lenses had good reviews and some very poor.

As for K mount lenses, even if you could make things work with flange distances and the like - you'd effectively be turning the 645D into a crop sensor camera. 35mm format lenses for SLR/DSLR cameras won't produce an image size to make use of that nice big medium format sensor.

For the money these lens are a pretty good deal for a lens you don't use too often. I haven't used mine for a while but I recall that I have stop it down a lot to get a sharp picture, especially at the edges. I think F11 or F16 is probable the best aperture. I get better results with the 4/3rds 8mm, which BTW is spectacular either wide open or stopped down, and sharp from edge to edge. I also have the old Zuiko 16mm which is pretty good but also not used much because of the edges and corners and light falloff (which is unavoidable).

I love shooting with my Arsat. Big, heavy chunk of metal and glass, it feels amazing. The only thing weird about it is that the focus ring has a lot of throw, so it can take a while to focus. I usually just zone focus with it, as the wide-angle brings almost everything into focus pretty easily. Also it has its own filter system, although you can un-thread the supplied filters and swap in your own 38mm ones.

I don't have a lot of photos to share right now as I have a bunch of rolls of color slide film in my freezer waiting to send out for processing. I have a few frames that came off a roll of B&W, although I'm new to film, and these are my first time ever shooting this film and processing it at home, so take that into consideration.I'm sure this lens is capable of more.